1. Field of the Invention
The present invention relates to an apparatus for detecting the shaking of stroke of a linear compressor, and more particularly, to an apparatus for detecting the shaking of the stroke of a linear compressor, which is capable of operating a linear compressor at the maximum efficiency point by detecting the shaking of the stroke using the amount of change in the phase differences of the stroke and current, and a method therefor.
2. Description of the Background Art
In general, a compressor increases the pressure of refrigerant vapor so that the refrigerant vapor evaporated by an evaporator can be easily condensed. Refrigerant circulates in a freezer, repeating processes of condensation and evaporation and carries heat from a cold place to a warm place due to the operation of the compressor.
Various types of compressors are used. However, the most efficient compressor is a linear compressor. The linear compressor compresses vapor by a piston that moves reciprocally in a cylinder to thus increase pressure. When the linear compressor is used in a refrigerator or an air conditioner, it is possible to change a compression ratio by changing a stroke voltage applied to the linear compressor, to thus control variable cooling capacity.
FIG. 1 is a block diagram showing the structure of a control apparatus of a conventional linear compressor.
As shown in FIG. 1, the control apparatus of the linear compressor includes a linear compressor 30, for controlling the cooing capacity (the caloric value taken away by surroundings when 1 Kg of refrigerant evaporates, while passing through the evaporator and performing a cooling operation), whose unit is Kcal/Kg, by changing the stroke due to the reciprocating motion of a piston, which is caused by the stroke voltage according to an initial stroke reference value, a voltage/current detector 40 for detecting the voltage and the current generated by the linear compressor 30 as the stroke increases due to the stroke voltage, a stroke calculator 50 for calculating the stroke using the voltage and the current detected from the voltage/current detector 40, a comparator 10 for receiving the stroke reference value calculated by the stroke calculator 50 at a predetermined point of time and the initial stroke reference value, comparing the stroke reference value with the initial stroke reference value, and outputting a comparison signal, and a stroke controller 20 for increasing or decreasing the stroke voltage according to the comparison signal of the comparator and applying the stroke voltage to the linear compressor 30.
In the linear compressor according to the conventional technology, the principle of the operation of the apparatus for detecting the shaking of the stroke will now be described with reference to FIG. 1.
When the stroke voltage according to the initial stroke reference value set by a user is output, the stroke varies according to the reciprocating motion of the piston inside the cylinder of the linear compressor 30. Accordingly, refrigerant gas inside the cylinder is discharged to a condenser through a discharge valve, to thus control the cooling capacity of the linear compressor. At this time, the voltage/current detector 40 detects the voltage and the current generated by the linear compressor 30 as the stroke increases due to the stroke voltage of the stroke controller 20 and inputs the detected voltage an current to the stroke calculator 50. Then, the stroke calculator 50 calculates the stroke at the predetermined point of time using the voltage and the current, which are detected by the voltage/current detector 40 and outputs the calculated value to the comparator 10.
The stroke is calculated as follows.   STROKE  =            1      α        ⁢          ∫                        (                                    V              M                        -                                          R                                  a                  ⁢                                      xe2x80x83                                    ⁢                  c                                            ⁢              i                        -                          L              ⁢                                                ⅆ                  i                                                  ⅆ                  t                                                              )                ⁢                  ⅆ          t                    
wherein, xcex1, VM, Rac, and   L  ⁢            ⅆ      i              ⅆ      t      
refer to a constant for converting electrical force into mechanical force, a voltage between both ends of a motor, a loss value due to resistance such as copper loss and core loss, and a voltage applied to an inductor in the motor, respectively.
The comparator 10 compares the stroke at the predetermined point of time, which is output from the stroke calculator 50 with the initial stroke reference value set by the user and inputs the comparison value to the stroke controller. The stroke controller 20 changes the stroke voltage according to the comparison value and applies the stroke voltage to the linear compressor 30.
At this time, the stroke controller 20 increases the stroke voltage when the stroke at the predetermined point of time, which is calculated by the stroke calculator 50, is smaller than the initial stroke reference value and reduces the stroke voltage when the stroke at the predetermined point of time is larger than the initial stroke reference value, to thus control the stroke voltage applied to the linear compressor 30.
The stroke controller 20 obtains difference between the previous stroke value of the linear compressor 30 and the stroke value at the predetermined point of time and determines that the shaking of the stroke (a phenomenon where the performance of the piston becomes unstable due to the characteristic of the compressor when the same input is applied by the specific stroke in a state where disturbance, that is, change in a voltage or noise does not exist) when the difference is no less than a reference value for determining whether the shaking of the stroke is detected. The stroke controller 20 obtains the difference between the previous current generated by the linear compressor 30 and the current at the predetermined point of time and determines that the shaking of the stroke occurs when the difference is no less than the reference value for determining whether the shaking of the stroke is detected. Accordingly, the stroke controller 20 increases or reduces the stroke voltage applied to the linear compressor 30.
That is, when the shaking of the stroke is detected in the air conditioner or the refrigerator that requires the large cooling capacity due to the controlling of a temperature by a user, the stroke controller 20 increases the stroke voltage so that the linear compressor 30 operates right above an area, in which the stroke shakes. When the shaking of the stroke is detected in the case where the small cooling capacity is required, the stroke controller 20 reduces the stroke voltage so that the linear compressor 30 operates right below the area, in which the stroke shakes.
However, according to the control apparatus of the conventional linear compressor, the maximum efficiency point of the operation of the compressor cannot be found out due to the change in an external voltage or external noise without being caused by the characteristic of the compressor because the shaking of the stroke is detected by the amount of change in the stroke or the current.
Therefore, an object of the present invention is to provide an apparatus for detecting the shaking of stroke of a linear compressor, which is capable of preventing the linear compressor from mis-operating due to change in an external voltage or noise by detecting the shaking of the stroke by the amount of change in the phase differences of the stroke and current, and a method therefor.
Another object of the present invention is to provide an apparatus for detecting the shaking of stroke of a linear compressor, which is capable of preventing the linear compressor from mis-operating due to change in an external voltage or noise by detecting the shaking of the stroke by the amount of change the phase differences of a voltage and current, and a method therefor.
Still another object of the present invention is to provide an apparatus for detecting the shaking of stroke of a linear compressor, which is capable of preventing the linear compressor from mis-operating due to change in an external voltage or noise by detecting the shaking of the stroke by the amount of change the phase differences of speed and current, and a method therefor.
To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, there is provided a control apparatus of a compressor, comprising a stroke/current phase difference calculator for calculating the phase differences of the stroke and current using the stroke and the current, which are determined by the increase and the reduction of the stroke due to the voltage generated by a linear compressor, a phase difference change amount calculator for calculating phase difference change amounts using the calculated phase differences of the stroke and the current, a shaking detector for comparing the calculated phase difference change amounts with a reference value for determining whether the shaking of the stroke is detected, to thus determine the shaking of the stroke, and a stroke controller for receiving a stroke shaking detection signal from the stroke shaking detector and changing the stroke voltage according to the magnitude of the request of cooling capacity, which is determined by the controlling of a temperature by a user, to thus control the driving of the linear compressor, during the operation of the linear compressor.
There is provided a method for detecting shaking of stroke of a linear compressor, comprising the steps of (a) calculating phase difference change amounts using the phase differences of stroke and current, (b) comparing the absolute values of the calculated phase difference change amounts with a reference value for determining whether the shaking of the stroke is detected; and (c) determining the shaking of the stroke by the step (b), changing a stroke voltage according to the magnitude of required cooling capacity, which is determined by the controlling of a temperature by a user, and driving the linear compressor.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.